Abstract

Background: Prostate cancer (PCa) is a common malignancy and a leading cause of cancer deaths among men in the United States. Abundant evidence has accumulated to suggest that epigenetic DNA methylation changes may appear earlier during PCa development than genetic changes, as well as more commonly and consistently suggesting that DNA methylated genes can be explored as DNA-based biomarker for PCa disease detection. Recently, we have identified NKX2-5 as a novel that is hypermethylated in prostate cancer. However, there is little information about the biological significance of this gene in prostate carcinogenesis. We hypothesize that NKX2-5 is a potential tumor suppressor gene that is frequently inactivated in prostate cancer. Methods: We carried out gain-and-loss functional studies of NKX2-5 in prostate cancer cell lines and validated expression at the RNA transcript level using quantitative RT-PCR. Protein expression was analyzed by western blotting and cell cycle analysis investigated by flow cytometer. Results: Over-expression of NKX2-5 was detrimental to prostate cancer cell proliferation as evidenced by significant inhibition of prostate cancer cell proliferation in comparison to control (vector only transfection) and this was due to cell arrest in Go/G1 phase and increase apoptosis. In contract, successful knockdown of NKX2-5 by shRNA transfection increased prostate cancer cell proliferation. Western blot analysis demonstrated that NKX2-5 plays a key regulatory role in the expression of several genes including p53, PTEN, Histone H1 and the androgen receptor. Conclusion: Our observation suggests that NKX2-5, a member of the homeobox gene family of plays an important tumor suppressor activity in prostate carcinogenesis. Because this gene plays important role in several signal transduction pathways, this gene can be exploited as potential biomarker for the early detection of prostate cancer and could be an attractive target to explore for drug investigation or gene therapies of prostate cancer.